The systemic vasculitides are a group of diseases characterized by severe inflammation of blood vessels leading to arterial stenosis or occlusion, and organ damage or death if untreated. With aggressive immunosuppressive treatment, most patients survive, but subsequent disease course is variable, relapse is common, and long-term morbidity from vasculitis or its treatment is expected. Long-term longitudinal studies are needed to inform and guide clinicians in this era of adequate but imperfect management. There are also significant unmet needs for i) biomarkers of disease activity, risk of relapse, and long-term damage; ii) genetic epidemiology studies to provide insight into pathogenesis and ideas for therapeutics; iii) early-phase clinical trials of novel therapeutics; iv) novel methods to conduct high-quality clinical trials and clinical research studies in these rare diseases; and v) for improved outcome measures, including patient-reported outcomes. The VCRC Longitudinal Studies address all these unmet needs through the multiple research studies associated with these protocols. The Vasculitis Clinical Research Consortium, initiated in 2004 under the auspices of the NIH Rare Diseases Clinical Research Network (RDCRN), encompasses longitudinal cohort studies of six vasculitides [giant cell arteritis (GCA), Takayasu's arteritis (TAK), polyarteritis nodosa (PAN), granulomatosis with polyangiitis (Wegener's, GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (Churg- Strauss, EGPA)] at leading referral centers in the US and Canada. More than 5000 patients have been enrolled. The VCRC Longitudinal Studies are central to the goals of this RDCRC and serve as the foundation for the exploration of new potential biomarkers of disease, phase II and 111 clinical trials, development of improved outcome measures, training of fellows in vasculitis research, and collaboration with patient support organizations. The Specific Aims of this project are to 1) support the continued successful conduct of the VCRC Longitudinal Studies of six vasculitides, 2) expand the Longitudinal Studies to include patients with isolated aortitis, and 3) maintain and expand the VCRC Biospecimen and Clinical Data Repositories for use by a broad range of scientists, both within and beyond the core group of Consortium investigators.